Document Detail


FTIR study of the retinal Schiff base and internal water molecules of proteorhodopsin.
MedLine Citation:
PMID:  17428036     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Proteorhodopsin (PR), an archaeal-type rhodopsin found in marine bacteria, is a light-driven proton pump similar to bacteriorhodopsin (BR). It is known that Asp97, a counterion of the protonated Schiff base, possesses a higher pKa ( approximately 7) compared to that of homologous Asp85 in BR (<3). This suggests that PR has a hydrogen-bonding network different from that of BR. We previously reported that a strongly hydrogen-bonded water molecule is observed only in the alkaline form of PR, where Asp97 is deprotonated (Furutani, Y., Ikeda, D., Shibata, M., and Kandori, H. (2006) Chem. Phys. 324, 705-708). This is probably correlated with the pH-dependent proton pumping activity of PR. In this work, we studied the water-containing hydrogen-bonding network in the Schiff base region of PR by means of Fourier-transform infrared (FTIR) spectroscopy at 77 K. [zeta-15N]Lys-labeling and 18O water were used for assigning the Schiff base N-D and water O-D stretching vibrations in D2O, respectively. The frequency upshift of the N-D stretch in the primary K intermediate is much smaller for PR than for BR, indicating that the Schiff base forms a hydrogen bond after retinal photoisomerization. We then measured FTIR spectra of the mutants of Asp97 (D97N and D97E) and Asp227 (D227N and D227E) to identify the amino acid interacting with the Schiff base in the K state. The PRK minus PR spectra of D97N and D97E were similar to those of the acidic and alkaline forms, respectively, of the wild type implying that the structural changes upon retinal photoisomerization are not influenced by the mutation at Asp97. In contrast, clear spectral differences were observed in D227N and D227E, including vibrational bands of the Schiff base and water molecules. It is concluded that Asp227 plays a crucial role during the photoisomerization process, though Asp97 acts as the primary counterion in the unphotolyzed state of PR.
Authors:
Daisuke Ikeda; Yuji Furutani; Hideki Kandori
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2007-04-12
Journal Detail:
Title:  Biochemistry     Volume:  46     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  2007 May 
Date Detail:
Created Date:  2007-05-01     Completed Date:  2007-05-31     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  United States    
Other Details:
Languages:  eng     Pagination:  5365-73     Citation Subset:  IM    
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
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MeSH Terms
Descriptor/Qualifier:
Archaeal Proteins / chemistry*,  genetics
Halobacterium salinarum / chemistry,  genetics
Hydrogen-Ion Concentration
Light Signal Transduction
Photolysis
Protons
Retinaldehyde / chemistry*
Rhodopsin / chemistry*,  genetics
Schiff Bases / chemistry
Spectroscopy, Fourier Transform Infrared
Water / chemistry*
Chemical
Reg. No./Substance:
0/Archaeal Proteins; 0/Protons; 0/Schiff Bases; 0/proteorhodopsin; 116-31-4/Retinaldehyde; 7732-18-5/Water; 9009-81-8/Rhodopsin

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